> Herbert,
>         Thanks I think this answers my question.  I'm happy as long as I
> can keep my valve and use less power.
>
> I would still like understand the concept behind PWM the valve.
>  (I get it's a simple squarewave freq)  But how does the 5V not kill the
> 1.2V coil?  And how does the coil stay open during low periods of the
> squarewave?

        What I am proposing only works because you are dealing with a
mechanical/physical system. What is happening is you are pulsing the 5V so
fast that the mechanical solonoid can't possibly react that quickly (think
of a light bulb, it is being "pulsed" at 120 times per second (in countries
with 60Hz grids) yet it doesn't flicker, this is because the bulb can't
possibly heat up and cool down that quickly. Flourescent bulbs on the other
hand CAN react that quickly and DO flicker (only they flicker at a rate so
fast the human eye doesn't notice, for the most part)). The 5V will not kill
the coil since it is there for a relatively short amount of time. I won't go
into the math of how all this works, you can however research this sort of
stuff on the web or at your local library.

> BTW, I do have the reverse diode there for protection.  :)  Although I
> do have this question.  I normally pick a diode with a large max voltage
> valve (say 200V), but how do I pick the max current valve?

        Generally you don't have to worry about it with typical solenoids, a 1A
part is usually sufficient. The current going through the part will be
significant, however it will be of very short duration. In order to properly
figure things out you would need alot more info and more math, and it
certainly is possible to figure out, I just don't think it would be worth it
in this case (unless you are building a million of them?). TTYL

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